indevs.texi

@chapter Input Devices
@c man begin INPUT DEVICES

Input devices are configured elements in FFmpeg which enable accessing
the data coming from a multimedia device attached to your system.

When you configure your FFmpeg build, all the supported input devices
are enabled by default. You can list all available ones using the
configure option "--list-indevs".

You can disable all the input devices using the configure option
"--disable-indevs", and selectively enable an input device using the
option "--enable-indev=@var{INDEV}", or you can disable a particular
input device using the option "--disable-indev=@var{INDEV}".

The option "-devices" of the ff* tools will display the list of
supported input devices.

A description of the currently available input devices follows.

@section alsa

ALSA (Advanced Linux Sound Architecture) input device.

To enable this input device during configuration you need libasound
installed on your system.

This device allows capturing from an ALSA device. The name of the
device to capture has to be an ALSA card identifier.

An ALSA identifier has the syntax:
@example
hw:@var{CARD}[,@var{DEV}[,@var{SUBDEV}]]
@end example

where the @var{DEV} and @var{SUBDEV} components are optional.

The three arguments (in order: @var{CARD},@var{DEV},@var{SUBDEV})
specify card number or identifier, device number and subdevice number
(-1 means any).

To see the list of cards currently recognized by your system check the
files @file{/proc/asound/cards} and @file{/proc/asound/devices}.

For example to capture with @command{ffmpeg} from an ALSA device with
card id 0, you may run the command:
@example
ffmpeg -f alsa -i hw:0 alsaout.wav
@end example

For more information see:
@url{http://www.alsa-project.org/alsa-doc/alsa-lib/pcm.html}

@section avfoundation

AVFoundation input device.

AVFoundation is the currently recommended framework by Apple for streamgrabbing on OSX >= 10.7 as well as on iOS.
The older QTKit framework has been marked deprecated since OSX version 10.7.

The input filename has to be given in the following syntax:
@example
-i "[[VIDEO]:[AUDIO]]"
@end example
The first entry selects the video input while the latter selects the audio input.
The stream has to be specified by the device name or the device index as shown by the device list.
Alternatively, the video and/or audio input device can be chosen by index using the
@option{
    -video_device_index <INDEX>
}
and/or
@option{
    -audio_device_index <INDEX>
}
, overriding any
device name or index given in the input filename.

All available devices can be enumerated by using @option{-list_devices true}, listing
all device names and corresponding indices.

There are two device name aliases:
@table @code

@item default
Select the AVFoundation default device of the corresponding type.

@item none
Do not record the corresponding media type.
This is equivalent to specifying an empty device name or index.

@end table

@subsection Options

AVFoundation supports the following options:

@table @option

@item -list_devices <TRUE|FALSE>
If set to true, a list of all available input devices is given showing all
device names and indices.

@item -video_device_index <INDEX>
Specify the video device by its index. Overrides anything given in the input filename.

@item -audio_device_index <INDEX>
Specify the audio device by its index. Overrides anything given in the input filename.

@item -pixel_format <FORMAT>
Request the video device to use a specific pixel format.
If the specified format is not supported, a list of available formats is given
und the first one in this list is used instead. Available pixel formats are:
@code{monob, rgb555be, rgb555le, rgb565be, rgb565le, rgb24, bgr24, 0rgb, bgr0, 0bgr, rgb0,
 bgr48be, uyvy422, yuva444p, yuva444p16le, yuv444p, yuv422p16, yuv422p10, yuv444p10,
 yuv420p, nv12, yuyv422, gray}

@end table

@subsection Examples

@itemize

@item
Print the list of AVFoundation supported devices and exit:
@example
$ ffmpeg -f avfoundation -list_devices true -i ""
@end example

@item
Record video from video device 0 and audio from audio device 0 into out.avi:
@example
$ ffmpeg -f avfoundation -i "0:0" out.avi
@end example

@item
Record video from video device 2 and audio from audio device 1 into out.avi:
@example
$ ffmpeg -f avfoundation -video_device_index 2 -i ":1" out.avi
@end example

@item
Record video from the system default video device using the pixel format bgr0 and do not record any audio into out.avi:
@example
$ ffmpeg -f avfoundation -pixel_format bgr0 -i "default:none" out.avi
@end example

@end itemize

@section bktr

BSD video input device.

@section dshow

Windows DirectShow input device.

DirectShow support is enabled when FFmpeg is built with the mingw-w64 project.
Currently only audio and video devices are supported.

Multiple devices may be opened as separate inputs, but they may also be
opened on the same input, which should improve synchronism between them.

The input name should be in the format:

@example
@var{TYPE}=@var{NAME}[:@var{TYPE}=@var{NAME}]
@end example

where @var{TYPE} can be either @var{audio} or @var{video},
and @var{NAME} is the device's name or alternative name..

@subsection Options

If no options are specified, the device's defaults are used.
If the device does not support the requested options, it will
fail to open.

@table @option

@item video_size
Set the video size in the captured video.

@item framerate
Set the frame rate in the captured video.

@item sample_rate
Set the sample rate (in Hz) of the captured audio.

@item sample_size
Set the sample size (in bits) of the captured audio.

@item channels
Set the number of channels in the captured audio.

@item list_devices
If set to @option{true}, print a list of devices and exit.

@item list_options
If set to @option{true}, print a list of selected device's options
and exit.

@item video_device_number
Set video device number for devices with same name (starts at 0,
defaults to 0).

@item audio_device_number
Set audio device number for devices with same name (starts at 0,
defaults to 0).

@item pixel_format
Select pixel format to be used by DirectShow. This may only be set when
the video codec is not set or set to rawvideo.

@item audio_buffer_size
Set audio device buffer size in milliseconds (which can directly
impact latency, depending on the device).
Defaults to using the audio device's
default buffer size (typically some multiple of 500ms).
Setting this value too low can degrade performance.
See also
@url{http://msdn.microsoft.com/en-us/library/windows/desktop/dd377582(v=vs.85).aspx}

@item video_pin_name
Select video capture pin to use by name or alternative name.

@item audio_pin_name
Select audio capture pin to use by name or alternative name.

@item crossbar_video_input_pin_number
Select video input pin number for crossbar device. This will be
routed to the crossbar device's Video Decoder output pin.
Note that changing this value can affect future invocations
(sets a new default) until system reboot occurs.

@item crossbar_audio_input_pin_number
Select audio input pin number for crossbar device. This will be
routed to the crossbar device's Audio Decoder output pin.
Note that changing this value can affect future invocations
(sets a new default) until system reboot occurs.

@item show_video_device_dialog
If set to @option{true}, before capture starts, popup a display dialog
to the end user, allowing them to change video filter properties
and configurations manually.
Note that for crossbar devices, adjusting values in this dialog
may be needed at times to toggle between PAL (25 fps) and NTSC (29.97)
input frame rates, sizes, interlacing, etc.  Changing these values can
enable different scan rates/frame rates and avoiding green bars at
the bottom, flickering scan lines, etc.
Note that with some devices, changing these properties can also affect future
invocations (sets new defaults) until system reboot occurs.

@item show_audio_device_dialog
If set to @option{true}, before capture starts, popup a display dialog
to the end user, allowing them to change audio filter properties
and configurations manually.

@item show_video_crossbar_connection_dialog
If set to @option{true}, before capture starts, popup a display
dialog to the end user, allowing them to manually
modify crossbar pin routings, when it opens a video device.

@item show_audio_crossbar_connection_dialog
If set to @option{true}, before capture starts, popup a display
dialog to the end user, allowing them to manually
modify crossbar pin routings, when it opens an audio device.

@item show_analog_tv_tuner_dialog
If set to @option{true}, before capture starts, popup a display
dialog to the end user, allowing them to manually
modify TV channels and frequencies.

@item show_analog_tv_tuner_audio_dialog
If set to @option{true}, before capture starts, popup a display
dialog to the end user, allowing them to manually
modify TV audio (like mono vs. stereo, Language A,B or C).

@end table

@subsection Examples

@itemize

@item
Print the list of DirectShow supported devices and exit:
@example
$ ffmpeg -list_devices true -f dshow -i dummy
@end example

@item
Open video device @var{Camera}:
@example
$ ffmpeg -f dshow -i video="Camera"
@end example

@item
Open second video device with name @var{Camera}:
@example
$ ffmpeg -f dshow -video_device_number 1 -i video="Camera"
@end example

@item
Open video device @var{Camera} and audio device @var{Microphone}:
@example
$ ffmpeg -f dshow -i video="Camera":audio="Microphone"
@end example

@item
Print the list of supported options in selected device and exit:
@example
$ ffmpeg -list_options true -f dshow -i video="Camera"
@end example

@item
Specify pin names to capture by name or alternative name, specify alternative device name:
@example
$ ffmpeg -f dshow -audio_pin_name "Audio Out" -video_pin_name 2 -i video=video="@@device_pnp_\\?\pci#ven_1a0a&dev_6200&subsys_62021461&rev_01#4&e2c7dd6&0&00e1#@{65e8773d-8f56-11d0-a3b9-00a0c9223196@}\@{ca465100-deb0-4d59-818f-8c477184adf6@}":audio="Microphone"
@end example

@item
Configure a crossbar device, specifying crossbar pins, allow user to adjust video capture properties at startup:
@example
$ ffmpeg -f dshow -show_video_device_dialog true -crossbar_video_input_pin_number 0
     -crossbar_audio_input_pin_number 3 -i video="AVerMedia BDA Analog Capture":audio="AVerMedia BDA Analog Capture"
@end example

@end itemize

@section dv1394

Linux DV 1394 input device.

@section fbdev

Linux framebuffer input device.

The Linux framebuffer is a graphic hardware-independent abstraction
layer to show graphics on a computer monitor, typically on the
console. It is accessed through a file device node, usually
@file{/dev/fb0}.

For more detailed information read the file
Documentation/fb/framebuffer.txt included in the Linux source tree.

To record from the framebuffer device @file{/dev/fb0} with
@command{ffmpeg}:
@example
ffmpeg -f fbdev -r 10 -i /dev/fb0 out.avi
@end example

You can take a single screenshot image with the command:
@example
ffmpeg -f fbdev -frames:v 1 -r 1 -i /dev/fb0 screenshot.jpeg
@end example

See also @url{http://linux-fbdev.sourceforge.net/}, and fbset(1).

@section gdigrab

Win32 GDI-based screen capture device.

This device allows you to capture a region of the display on Windows.

There are two options for the input filename:
@example
desktop
@end example
or
@example
title=@var{window_title}
@end example

The first option will capture the entire desktop, or a fixed region of the
desktop. The second option will instead capture the contents of a single
window, regardless of its position on the screen.

For example, to grab the entire desktop using @command{ffmpeg}:
@example
ffmpeg -f gdigrab -framerate 6 -i desktop out.mpg
@end example

Grab a 640x480 region at position @code{10,20}:
@example
ffmpeg -f gdigrab -framerate 6 -offset_x 10 -offset_y 20 -video_size vga -i desktop out.mpg
@end example

Grab the contents of the window named "Calculator"
@example
ffmpeg -f gdigrab -framerate 6 -i title=Calculator out.mpg
@end example

@subsection Options

@table @option
@item draw_mouse
Specify whether to draw the mouse pointer. Use the value @code{0} to
not draw the pointer. Default value is @code{1}.

@item framerate
Set the grabbing frame rate. Default value is @code{ntsc},
corresponding to a frame rate of @code{30000/1001}.

@item show_region
Show grabbed region on screen.

If @var{show_region} is specified with @code{1}, then the grabbing
region will be indicated on screen. With this option, it is easy to
know what is being grabbed if only a portion of the screen is grabbed.

Note that @var{show_region} is incompatible with grabbing the contents
of a single window.

For example:
@example
ffmpeg -f gdigrab -show_region 1 -framerate 6 -video_size cif -offset_x 10 -offset_y 20 -i desktop out.mpg
@end example

@item video_size
Set the video frame size. The default is to capture the full screen if @file{desktop} is selected, or the full window size if @file{title=@var{window_title}} is selected.

@item offset_x
When capturing a region with @var{video_size}, set the distance from the left edge of the screen or desktop.

Note that the offset calculation is from the top left corner of the primary monitor on Windows. If you have a monitor positioned to the left of your primary monitor, you will need to use a negative @var{offset_x} value to move the region to that monitor.

@item offset_y
When capturing a region with @var{video_size}, set the distance from the top edge of the screen or desktop.

Note that the offset calculation is from the top left corner of the primary monitor on Windows. If you have a monitor positioned above your primary monitor, you will need to use a negative @var{offset_y} value to move the region to that monitor.

@end table

@section iec61883

FireWire DV/HDV input device using libiec61883.

To enable this input device, you need libiec61883, libraw1394 and
libavc1394 installed on your system. Use the configure option
@code{--enable-libiec61883} to compile with the device enabled.

The iec61883 capture device supports capturing from a video device
connected via IEEE1394 (FireWire), using libiec61883 and the new Linux
FireWire stack (juju). This is the default DV/HDV input method in Linux
Kernel 2.6.37 and later, since the old FireWire stack was removed.

Specify the FireWire port to be used as input file, or "auto"
to choose the first port connected.

@subsection Options

@table @option

@item dvtype
Override autodetection of DV/HDV. This should only be used if auto
detection does not work, or if usage of a different device type
should be prohibited. Treating a DV device as HDV (or vice versa) will
not work and result in undefined behavior.
The values @option{auto}, @option{dv} and @option{hdv} are supported.

@item dvbuffer
Set maximum size of buffer for incoming data, in frames. For DV, this
is an exact value. For HDV, it is not frame exact, since HDV does
not have a fixed frame size.

@item dvguid
Select the capture device by specifying it's GUID. Capturing will only
be performed from the specified device and fails if no device with the
given GUID is found. This is useful to select the input if multiple
devices are connected at the same time.
Look at /sys/bus/firewire/devices to find out the GUIDs.

@end table

@subsection Examples

@itemize

@item
Grab and show the input of a FireWire DV/HDV device.
@example
ffplay -f iec61883 -i auto
@end example

@item
Grab and record the input of a FireWire DV/HDV device,
using a packet buffer of 100000 packets if the source is HDV.
@example
ffmpeg -f iec61883 -i auto -hdvbuffer 100000 out.mpg
@end example

@end itemize

@section jack

JACK input device.

To enable this input device during configuration you need libjack
installed on your system.

A JACK input device creates one or more JACK writable clients, one for
each audio channel, with name @var{client_name}:input_@var{N}, where
@var{client_name} is the name provided by the application, and @var{N}
is a number which identifies the channel.
Each writable client will send the acquired data to the FFmpeg input
device.

Once you have created one or more JACK readable clients, you need to
connect them to one or more JACK writable clients.

To connect or disconnect JACK clients you can use the @command{jack_connect}
and @command{jack_disconnect} programs, or do it through a graphical interface,
for example with @command{qjackctl}.

To list the JACK clients and their properties you can invoke the command
@command{jack_lsp}.

Follows an example which shows how to capture a JACK readable client
with @command{ffmpeg}.
@example
# Create a JACK writable client with name "ffmpeg".
$ ffmpeg -f jack -i ffmpeg -y out.wav

# Start the sample jack_metro readable client.
$ jack_metro -b 120 -d 0.2 -f 4000

# List the current JACK clients.
$ jack_lsp -c
system:capture_1
system:capture_2
system:playback_1
system:playback_2
ffmpeg:input_1
metro:120_bpm

# Connect metro to the ffmpeg writable client.
$ jack_connect metro:120_bpm ffmpeg:input_1
@end example

For more information read:
@url{http://jackaudio.org/}

@section lavfi

Libavfilter input virtual device.

This input device reads data from the open output pads of a libavfilter
filtergraph.

For each filtergraph open output, the input device will create a
corresponding stream which is mapped to the generated output. Currently
only video data is supported. The filtergraph is specified through the
option @option{graph}.

@subsection Options

@table @option

@item graph
Specify the filtergraph to use as input. Each video open output must be
labelled by a unique string of the form "out@var{N}", where @var{N} is a
number starting from 0 corresponding to the mapped input stream
generated by the device.
The first unlabelled output is automatically assigned to the "out0"
label, but all the others need to be specified explicitly.

The suffix "+subcc" can be appended to the output label to create an extra
stream with the closed captions packets attached to that output
(experimental; only for EIA-608 / CEA-708 for now).
The subcc streams are created after all the normal streams, in the order of
the corresponding stream.
For example, if there is "out19+subcc", "out7+subcc" and up to "out42", the
stream #43 is subcc for stream #7 and stream #44 is subcc for stream #19.

If not specified defaults to the filename specified for the input
device.

@item graph_file
Set the filename of the filtergraph to be read and sent to the other
filters. Syntax of the filtergraph is the same as the one specified by
the option @var{graph}.

@end table

@subsection Examples

@itemize
@item
Create a color video stream and play it back with @command{ffplay}:
@example
ffplay -f lavfi -graph "color=c=pink [out0]" dummy
@end example

@item
As the previous example, but use filename for specifying the graph
description, and omit the "out0" label:
@example
ffplay -f lavfi color=c=pink
@end example

@item
Create three different video test filtered sources and play them:
@example
ffplay -f lavfi -graph "testsrc [out0]; testsrc,hflip [out1]; testsrc,negate [out2]" test3
@end example

@item
Read an audio stream from a file using the amovie source and play it
back with @command{ffplay}:
@example
ffplay -f lavfi "amovie=test.wav"
@end example

@item
Read an audio stream and a video stream and play it back with
@command{ffplay}:
@example
ffplay -f lavfi "movie=test.avi[out0];amovie=test.wav[out1]"
@end example

@item
Dump decoded frames to images and closed captions to a file (experimental):
@example
ffmpeg -f lavfi -i "movie=test.ts[out0+subcc]" -map v frame%08d.png -map s -c copy -f rawvideo subcc.bin
@end example

@end itemize

@section libcdio

Audio-CD input device based on libcdio.

To enable this input device during configuration you need libcdio
installed on your system. It requires the configure option
@code{--enable-libcdio}.

This device allows playing and grabbing from an Audio-CD.

For example to copy with @command{ffmpeg} the entire Audio-CD in @file{/dev/sr0},
you may run the command:
@example
ffmpeg -f libcdio -i /dev/sr0 cd.wav
@end example

@subsection Options
@table @option
@item speed
Set drive reading speed. Default value is 0.

The speed is specified CD-ROM speed units. The speed is set through
the libcdio @code{cdio_cddap_speed_set} function. On many CD-ROM
drives, specifying a value too large will result in using the fastest
speed.

@item paranoia_mode
Set paranoia recovery mode flags. It accepts one of the following values:

@table @samp
@item disable
@item verify
@item overlap
@item neverskip
@item full
@end table

Default value is @samp{disable}.

For more information about the available recovery modes, consult the
paranoia project documentation.
@end table

@section libdc1394

IIDC1394 input device, based on libdc1394 and libraw1394.

Requires the configure option @code{--enable-libdc1394}.

@section openal

The OpenAL input device provides audio capture on all systems with a
working OpenAL 1.1 implementation.

To enable this input device during configuration, you need OpenAL
headers and libraries installed on your system, and need to configure
FFmpeg with @code{--enable-openal}.

OpenAL headers and libraries should be provided as part of your OpenAL
implementation, or as an additional download (an SDK). Depending on your
installation you may need to specify additional flags via the
@code{--extra-cflags} and @code{--extra-ldflags} for allowing the build
system to locate the OpenAL headers and libraries.

An incomplete list of OpenAL implementations follows:

@table @strong
@item Creative
The official Windows implementation, providing hardware acceleration
with supported devices and software fallback.
See @url{http://openal.org/}.
@item OpenAL Soft
Portable, open source (LGPL) software implementation. Includes
backends for the most common sound APIs on the Windows, Linux,
Solaris, and BSD operating systems.
See @url{http://kcat.strangesoft.net/openal.html}.
@item Apple
OpenAL is part of Core Audio, the official Mac OS X Audio interface.
See @url{http://developer.apple.com/technologies/mac/audio-and-video.html}
@end table

This device allows one to capture from an audio input device handled
through OpenAL.

You need to specify the name of the device to capture in the provided
filename. If the empty string is provided, the device will
automatically select the default device. You can get the list of the
supported devices by using the option @var{list_devices}.

@subsection Options

@table @option

@item channels
Set the number of channels in the captured audio. Only the values
@option{1} (monaural) and @option{2} (stereo) are currently supported.
Defaults to @option{2}.

@item sample_size
Set the sample size (in bits) of the captured audio. Only the values
@option{8} and @option{16} are currently supported. Defaults to
@option{16}.

@item sample_rate
Set the sample rate (in Hz) of the captured audio.
Defaults to @option{44.1k}.

@item list_devices
If set to @option{true}, print a list of devices and exit.
Defaults to @option{false}.

@end table

@subsection Examples

Print the list of OpenAL supported devices and exit:
@example
$ ffmpeg -list_devices true -f openal -i dummy out.ogg
@end example

Capture from the OpenAL device @file{DR-BT101 via PulseAudio}:
@example
$ ffmpeg -f openal -i 'DR-BT101 via PulseAudio' out.ogg
@end example

Capture from the default device (note the empty string '' as filename):
@example
$ ffmpeg -f openal -i '' out.ogg
@end example

Capture from two devices simultaneously, writing to two different files,
within the same @command{ffmpeg} command:
@example
$ ffmpeg -f openal -i 'DR-BT101 via PulseAudio' out1.ogg -f openal -i 'ALSA Default' out2.ogg
@end example
Note: not all OpenAL implementations support multiple simultaneous capture -
try the latest OpenAL Soft if the above does not work.

@section oss

Open Sound System input device.

The filename to provide to the input device is the device node
representing the OSS input device, and is usually set to
@file{/dev/dsp}.

For example to grab from @file{/dev/dsp} using @command{ffmpeg} use the
command:
@example
ffmpeg -f oss -i /dev/dsp /tmp/oss.wav
@end example

For more information about OSS see:
@url{http://manuals.opensound.com/usersguide/dsp.html}

@section pulse

PulseAudio input device.

To enable this output device you need to configure FFmpeg with @code{--enable-libpulse}.

The filename to provide to the input device is a source device or the
string "default"

To list the PulseAudio source devices and their properties you can invoke
the command @command{pactl list sources}.

More information about PulseAudio can be found on @url{http://www.pulseaudio.org}.

@subsection Options
@table @option
@item server
Connect to a specific PulseAudio server, specified by an IP address.
Default server is used when not provided.

@item name
Specify the application name PulseAudio will use when showing active clients,
by default it is the @code{LIBAVFORMAT_IDENT} string.

@item stream_name
Specify the stream name PulseAudio will use when showing active streams,
by default it is "record".

@item sample_rate
Specify the samplerate in Hz, by default 48kHz is used.

@item channels
Specify the channels in use, by default 2 (stereo) is set.

@item frame_size
Specify the number of bytes per frame, by default it is set to 1024.

@item fragment_size
Specify the minimal buffering fragment in PulseAudio, it will affect the
audio latency. By default it is unset.
@end table

@subsection Examples
Record a stream from default device:
@example
ffmpeg -f pulse -i default /tmp/pulse.wav
@end example

@section qtkit

QTKit input device.

The filename passed as input is parsed to contain either a device name or index.
The device index can also be given by using -video_device_index.
A given device index will override any given device name.
If the desired device consists of numbers only, use -video_device_index to identify it.
The default device will be chosen if an empty string  or the device name "default" is given.
The available devices can be enumerated by using -list_devices.

@example
ffmpeg -f qtkit -i "0" out.mpg
@end example

@example
ffmpeg -f qtkit -video_device_index 0 -i "" out.mpg
@end example

@example
ffmpeg -f qtkit -i "default" out.mpg
@end example

@example
ffmpeg -f qtkit -list_devices true -i ""
@end example

@section sndio

sndio input device.

To enable this input device during configuration you need libsndio
installed on your system.

The filename to provide to the input device is the device node
representing the sndio input device, and is usually set to
@file{/dev/audio0}.

For example to grab from @file{/dev/audio0} using @command{ffmpeg} use the
command:
@example
ffmpeg -f sndio -i /dev/audio0 /tmp/oss.wav
@end example

@section video4linux2, v4l2

Video4Linux2 input video device.

"v4l2" can be used as alias for "video4linux2".

If FFmpeg is built with v4l-utils support (by using the
@code{--enable-libv4l2} configure option), it is possible to use it with the
@code{-use_libv4l2} input device option.

The name of the device to grab is a file device node, usually Linux
systems tend to automatically create such nodes when the device
(e.g. an USB webcam) is plugged into the system, and has a name of the
kind @file{/dev/video@var{N}}, where @var{N} is a number associated to
the device.

Video4Linux2 devices usually support a limited set of
@var{width}x@var{height} sizes and frame rates. You can check which are
supported using @command{-list_formats all} for Video4Linux2 devices.
Some devices, like TV cards, support one or more standards. It is possible
to list all the supported standards using @command{-list_standards all}.

The time base for the timestamps is 1 microsecond. Depending on the kernel
version and configuration, the timestamps may be derived from the real time
clock (origin at the Unix Epoch) or the monotonic clock (origin usually at
boot time, unaffected by NTP or manual changes to the clock). The
@option{-timestamps abs} or @option{-ts abs} option can be used to force
conversion into the real time clock.

Some usage examples of the video4linux2 device with @command{ffmpeg}
and @command{ffplay}:
@itemize
@item
List supported formats for a video4linux2 device:
@example
ffplay -f video4linux2 -list_formats all /dev/video0
@end example

@item
Grab and show the input of a video4linux2 device:
@example
ffplay -f video4linux2 -framerate 30 -video_size hd720 /dev/video0
@end example

@item
Grab and record the input of a video4linux2 device, leave the
frame rate and size as previously set:
@example
ffmpeg -f video4linux2 -input_format mjpeg -i /dev/video0 out.mpeg
@end example
@end itemize

For more information about Video4Linux, check @url{http://linuxtv.org/}.

@subsection Options

@table @option
@item standard
Set the standard. Must be the name of a supported standard. To get a
list of the supported standards, use the @option{list_standards}
option.

@item channel
Set the input channel number. Default to -1, which means using the
previously selected channel.

@item video_size
Set the video frame size. The argument must be a string in the form
@var{WIDTH}x@var{HEIGHT} or a valid size abbreviation.

@item pixel_format
Select the pixel format (only valid for raw video input).

@item input_format
Set the preferred pixel format (for raw video) or a codec name.
This option allows one to select the input format, when several are
available.

@item framerate
Set the preferred video frame rate.

@item list_formats
List available formats (supported pixel formats, codecs, and frame
sizes) and exit.

Available values are:
@table @samp
@item all
Show all available (compressed and non-compressed) formats.

@item raw
Show only raw video (non-compressed) formats.

@item compressed
Show only compressed formats.
@end table

@item list_standards
List supported standards and exit.

Available values are:
@table @samp
@item all
Show all supported standards.
@end table

@item timestamps, ts
Set type of timestamps for grabbed frames.

Available values are:
@table @samp
@item default
Use timestamps from the kernel.

@item abs
Use absolute timestamps (wall clock).

@item mono2abs
Force conversion from monotonic to absolute timestamps.
@end table

Default value is @code{default}.
@end table

@section vfwcap